The inventive concepts relate to the fabricating of transistors and semiconductor devices including the same. In particular, the inventive concepts relate to the fabricating of NMOS transistors and semiconductor devices, such as, for example, CMOS devices, that include NMOS transistors.
A conventional MOSFET (metal-oxide-semiconductor field effect transistor) is fabricated by forming a gate electrode structure at the upper portion of a semiconductor substrate, such as a single-crystalline substrate, and source and drain regions on opposite sides of the gate electrode strucuture. The gate electrode structure generally includes a gate separated from the semiconductor substrate by a thin insulating layer. When a sufficient voltage is applied to the gate electrode, the electric field generated penetrates the insulating layer and creates a channel, through which current can pass, in a region of the semiconductor substate below the gate electrode structure. The channel extends between the source and the drain regions. The source region is so named because it is the source of the charge carriers that flow through the channel. The drain is where the charge carriers leave the channel.
In a conventional NMOS, the source and drain regions are n+ regions of the substrate, and the charge carriers are electrons. It is know to enhance the mobility of the charge carriers, i.e. the electrons, in an NMOS transistor using a technique known as a stress memorization technique (SMT). In one such technique, a silicon oxide (SiO2) buffer layer and a silicon nitride (SiN) tensile stress layer are sequentially formed on the substrate over the gate electrode structure and the source/drain regions. The substrate is then thermally treated which increases the tensile stress in the SiN layer. As a result, the stress in the SiN layer is “memorized” as compressive stress in the source and drain regions. The compressive stress in the source and drain regions, in turn, induces tensile stress in the channel region, and the tensile stress allows for increased mobility of the electrons through the channel.